Accounting Policies (Accounting Pronouncements) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unfavorable impact on pre-tax operating results		$ (11.3)	$ 41.4	$ (34.4)	$ 173.7
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Projected impact of new accounting principle on prior period operating income						$ 70.6
Forecast | Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unfavorable impact on pre-tax operating results	$ 5.0